1. Field of the Invention
The invention relates to a surface-modified, pyrogenically produced titanium dioxide, a process for its production as well as its use.
2. Description of the Background
It is known that highly-disperse pyrogenic titanium dioxide (for example, titanium dioxide P 25 S from Degussa-Hxc3xcls AG), on account of its low average primary particle size (21 nm) and of the structure of the aggregates and agglomerates resulting from the pyrogenic production process, has advantageous properties as a UV-A and UV-B blocker in cosmetic sunblock preparations. In addition, it is known that an increasing degree of dispersion of the titanium dioxide has a favourable effect on the UV-blocking action.
The hydrophilic surface of the pyrogenically produced titanium dioxide necessitates the use of high shear forces in order to achieve a high degree of dispersion, above all in oleophilic preparations. Consequently, pyrogenically produced titanium dioxides already surface-modified with alkylsilyl groups are known (titanium dioxide T 805 from Degussa-Hxc3xcls Aktiengesellschaft) which, in addition to the improved dispersibility in oleophilic preparations even at low shear energies, also bring about an improved UV-blocking and a decreased photochemical activity in the pyrogenic titanium dioxide. (Technical Information TI 1176 xe2x80x9cHighly dispersed Titanium Dioxide for sunblock preparationsxe2x80x9d).
A disadvantage of the known surface-modified pyrogenic titanium dioxides is the low interaction with hydrophilic constituents of the cosmetic sunblock preparations, which is due to the exclusively oleophilic character of the surface.
The object of the invention is the development of a pyrogenically produced titanium dioxide, the surface modification of which imparts to it an oleophilic as well as a hydrophilic character, and which exhibits a good dispersibility in hydrophilic and in oleophilic media.
The invention provides surface-modified, pyrogenically produced titanium dioxide, which is characterized in that it is treated with at least one ammonium-functional silane.